Even if you are in your 20s you SHOULD know who Morrissey is, if you have deep love of music, particularly Indie music but his influence isn't restricted to just that genre nor indeed Manchester. But for starters on a very basic level: No Smiths = No Stone Roses = No Oasis (though perhaps more for the Johnny Marr side of things)
However Morrissey's lyrics were intellectual, challenging and political - perhaps in a way that punk had first started but he took it one step further in depth. He was closer to an old style traditional poet than a pop star. He did tend to sing about miserable people and the dreariness of life. He therefore tended to appeal to intelligent moody teenagers who wanted to stay in their bedroom and thought the world hated them - but often missed the sarcasm, witt and irony of his lyrics. He was probably inspired the whole Emo movement.
You don't actually have to like Morrissey's music; you just need to know who Morrissey is. Morrissey and The Smiths are one of the major junctions on the road map of British Music. I definitely wouldn't put him above Bowie on the influence list, but he does deserve a pretty high rank.
I go between phases of liking what he did, and thinking The Smiths/Morrissey are utter dirge.
His unique way of singing that bore no relation to the tune is brilliant; in fact you can sing any article from the newspaper in Morrissey fashion to pretty much any Smiths tune and it fits.
On a personal level though Morrissey was and definitely still is a Professional Cunt who makes a living out of being Miserable Bastard with the sensitivity of a T-Rex in a China Shop (forget the bull, hes on a whole different scale).
His controversial views have led to him being labelled as a racist (he had an ongoing dispute with NME for years until they finally settled up out of court when Morrissey decided he probably should get a bit more publicity for his flagging career and could be bothered to get round to suing them four years after making the comments that sparked this particular controversy, though he'd made remarks in a similar vein for many years previously). He's possibly the most well known and vocal anti-royalist, so his remarks about Kate aren't unexpected. He's a militant vegetarian and has said he understood why activists use violence and last year made this tasteful remark two days after the Brevik Massacre "We all live in a murderous world, as the events in Norway have shown, with 97 dead. Though that is nothing compared to what happens in McDonald's and Kentucky Fried Chicken every day."
As I say. Cunt. Of the Highest Order of Cunts.
And thats probably how he'll be remembered rather than as being a musician.
Pretty sad legacy for a man of his talent tbh.